There is a need to protect circuits, particularly circuits having a bridge rectifier module and a power factor correction (PFC) module from surge events/impulses in a power supply. Such surge events may be caused by lightning strikes or increases in a mains supply, for example.
Known ways of protecting against surge events include using at least two elements: a varistor between mains connectors and the bridge rectifier; and a bulk capacitor either directly behind the bridge rectifier or in parallel across the outputs of a PFC module. Further details of such surge protection is provided below in relation to FIG. 2.
One or more embodiments of the invention described herein can provide an improved surge protection circuit over the prior art, particularly for prior art circuits where there is no current path between the input voltage and a bulk capacitor. The improvement can lie in the use of fewer, and possibly the need for lower quality/specification, components than the prior art in order to provide adequate surge protection.
The listing or discussion of a prior-published document or any background in this specification should not necessarily be taken as an acknowledgement that the document or background is part of the state of the art or is common general knowledge.
According to a first aspect of the invention, there is provided a surge protection circuit for a circuit comprising a rectification module, the surge protection circuit comprising:
a first diode;
a second diode;
a capacitor; and
a discharge device; wherein
a first terminal of the first diode is connectable to a first input of the rectification module, a first terminal of the second diode is connectable to a second input of the rectification module, second terminals of the first and second diodes are both connected to the first plate of the capacitor, and the second plate of the capacitor is connectable to one of the outputs of the rectification module; and wherein:
the capacitor is configured such that it is consistently charged to substantially a peak value of a supply voltage during normal operation; and
the discharge device is connected to the capacitor and is configured to discharge the capacitor when the voltage across the capacitor is in excess of the peak value of the maximum supply voltage and not substantially discharge the capacitor when the voltage across the capacitor is not in excess of the peak value of the supply voltage during normal operation.
In some examples, the first and second diodes could be provided as part of a further bridge rectifier provided in parallel with the rectification module or as separate discrete components. It will be appreciated that the provision of the first and second diodes does not preclude the option of further diodes also being provided, for example the provision of a third and fourth diode as part of a further bridge rectifier.
The first terminals of the diodes may be the anode of the diodes, and the second terminals of the diodes may be the cathodes, or vice versa. The orientation of the diodes can be selected so as to provide a closed circuit for charging the capacitor from the mains supply, whereby the closed circuit includes a diode of the rectification module connected to one of the plates of the capacitor, and the first and second diodes are connected to the other plate of the capacitor.
There may be provided a surge protection circuit for a circuit comprising a rectification module, the surge protection circuit comprising:
a first diode;
a second diode;
a capacitor; and
a discharge device; wherein
the anode of the first diode is connectable to a first input of the rectification module, the anode of the second diode is connectable to a second input of the rectification module, the cathodes of the first and second diodes are both connected to the first plate of the capacitor, and the second plate of the capacitor is connectable to the negative output of the rectification module; and wherein:
the capacitor is configured such that it is consistently charged to substantially a peak value of a supply voltage during normal operation; and
the discharge device is connected to the first plate of the capacitor and is configured to discharge the capacitor when the voltage across the capacitor is in excess of the peak value of the maximum supply voltage and not substantially discharge the capacitor when the voltage across the capacitor is not in excess of the peak value of the supply voltage during normal operation.
There may be provided a surge protection circuit for a circuit comprising a rectification module, the surge protection circuit comprising:
a first diode;
a second diode;
a capacitor; and
a discharge device; wherein
the cathode of the first diode is connectable to a first input of the rectification module, the cathode of the second diode is connectable to a second input of the rectification module, the anodes of the first and second diodes are both connected to the first plate of the capacitor, and the second plate of the capacitor is connectable to the positive output of the rectification module; and wherein:
the capacitor is configured such that it is consistently charged to substantially a peak value of a supply voltage during normal operation; and
the discharge device is connected to the second plate of the capacitor and is configured to discharge the capacitor when the voltage across the capacitor is in excess of the peak value of the maximum supply voltage and not substantially discharge the capacitor when the voltage across the capacitor is not in excess of the peak value of the supply voltage during normal operation.